Wake-up signal management

ABSTRACT

The invention relates to a method for a wireless communication apparatus, and such an apparatus, configured to use a wake-up signal (WUS), transmitted for waking up a main receiver of a wireless communication device responsive to detection of the WUS by a wake-up receiver (WUR) of the wireless communication device. The method comprises controlling a bandwidth associated with the WUS based on a reception condition metric for the WUR. Embodiments may comprise determining the reception condition metric for the WUR by correlating a received signal comprising the WUS with a WUS reference signal to provide an extreme correlation value, and determining the reception condition metric for the WUR based on the extreme correlation value. In some embodiments, controlling the bandwidth associated with the WUS based on the reception condition metric may comprise controlling a WUS bandwidth based on the reception condition metric. The wireless communication apparatus may be the wireless communication device or the access point.

TECHNICAL FIELD

The present disclosure relates generally to the field of wirelesscommunication. More particularly, it relates to wake-up signals forwaking up a main receiver of a wireless communication device.

BACKGROUND

A wake-up receiver (WUR; sometimes referred to as a wake-up radio)provides for significant reduction of the power consumption in wirelesscommunication receivers. One aspect of the WUR concept is that the WURcan be based on a very relaxed architecture, since it only needs to beable to detect presence of a wake-up signal (WUS) and may not be usedfor reception of data or other control signaling than the WUS.

A commonly used modulation for the WUS (i.e., the signal sent to theWUR) is on-off keying (OOK). OOK is a binary modulation, where a logicalone is represented by sending a signal (ON) and a logical zero isrepresented by not sending any signal (OFF), or vice versa.

Ongoing activities in the Institute of Electrical and ElectronicsEngineers (IEEE) 802.11 task group (TG) named IEEE 802.11ba aims atstandardization of the physical (PHY) layer and the media access control(MAC) layer for a WUR that is to be used as a companion radio to themain IEEE 802.11 radio to significantly reduce the average powerconsumption by ensuring that the main radio can be in a low power modemore often.

A possibility for generation of the WUS is using an inverse fast Fouriertransform (IFFT), since such a functional block is already available inmany transmitters, for example Wi-Fi transmitters supporting e.g. IEEE802.11a/g/n/ac. One example approach to generation of the WUS using OOKis to use 13 sub-carriers in the center of a frequency range of theIFFT, to populate them with a suitable signal to represent ON and to nottransmit anything at all on these sub-carriers to represent OFF. In atypical example, the IFFT has 64 points and is operating at a samplingrate of 20 MHz. Just as for ordinary orthogonal frequency divisionmultiplexing (OFDM), a cyclic prefix (CP) may be added after the IFFToperation in order to have the same duration and format as a normal OFDMsymbol duration used in 802.11a/g/n/ac (and thus be able to spoof legacystations by prepending a legacy preamble at the beginning of the WUS).In this way, legacy stations will be able to detect the transmission ofa WUS and correctly defer access to the wireless medium. That is, legacystations will be able to detect presence of a WUS although they willgenerally not be able to decode the information carried by the WUS.

Although the approach described above has many attractive features, itsuffers from a relatively poor sensitivity, potentially making the WUSdifficult to receive for a low power implementation of a WUR.

Therefore, there is a need for approaches that enable WUS receptionunder non-favorable reception conditions while also being powerefficient.

As background prior art, the document US 2007/0264963 A1 can bementioned. It relates to a method and system employing wideband signalsfor RF wakeup. A method of reducing an energy consumption of a wirelessnetwork is disclosed. The method includes periodically entering a sleepmode by a receiver node, broadcasting a signal simultaneously across awide band frequency range, upon waking up from the sleep mode, listeningby the receiver node to only a first narrow part of the wide bandfrequency range, the receiver node subsequently either returning tosleep if a signal strength of the broadcasted signal is less than apredefined signal strength threshold, or staying awake for an additionalperiod of time if the signal strength of the broadcasted signal isgreater than the predefined signal strength threshold. The idea is toreduce power by listening to a narrowband part of a wideband signal. Inparticular the receiver can select which part to use, and thetransmitter does not need to know.

Another background document is US 2012/0120859 A1. It relates totechniques for wakeup signaling for a very low power WLAN device. Adisclosed embodiment provides a method of wakeup signaling for a verylow power wireless local area network device (WLAN) device, comprisingtransmitting by an access point operable in the WLAN of a wake-up signalthat can be received using low-power techniques at a receiver associatedwith the device. The idea appears to be to use spare tones in 802.11 totransmit the WUS.

SUMMARY

It should be emphasized that the term “comprises/comprising” when usedin this specification is taken to specify the presence of statedfeatures, integers, steps, or components, but does not preclude thepresence or addition of one or more other features, integers, steps,components, or groups thereof. As used herein, the singular forms “a”,“an” and “the” are intended to include the plural forms as well, unlessthe context clearly indicates otherwise.

It is an object of some embodiments to solve or mitigate, alleviate, oreliminate at least some of the disadvantages referred to herein, orother disadvantages.

According to a first aspect, this is achieved by a method for a wirelesscommunication apparatus configured to use a wake-up signal (WUS),transmitted, e.g. by an access point, for waking up a main receiver of awireless communication device responsive to detection of the WUS by awake-up receiver (WUR) of the wireless communication device.

The method comprises controlling a bandwidth associated with the WUSbased on a reception condition metric for the WUR.

The wireless communication apparatus may be the wireless communicationdevice according to some embodiments.

The method may, according to some embodiments, further comprisedetermining the reception condition metric for the WUR by correlating areceived signal comprising the WUS with a WUS reference signal toprovide an extreme (e.g. maximum or minimum) correlation value, anddetermining the reception condition metric for the WUR based on theresult of this correlation, e.g, by considering the extreme correlationvalue.

Determining the reception condition metric for the WUR based on theextreme correlation value may, in some embodiments, comprise comparingthe extreme correlation value to a reception condition threshold value,determining the reception condition metric to have a first receptioncondition value when the extreme correlation value is higher than thereception condition threshold value and determining the receptioncondition metric to have a second reception condition value when theextreme correlation value is not higher than the reception conditionthreshold value.

The method may further comprise dynamically adapting the receptioncondition threshold value based on an immediately previous bandwidthassociated with the WUS according to some embodiments.

In some embodiments, the method may further comprise comparing theextreme correlation value to a WUS detection threshold value which islower than the reception condition threshold, and waking up the mainreceiver when the extreme correlation value is larger than the WUSdetection threshold value.

The WUR may, according to some embodiments, comprise a channel selectivefilter for filtering of the WUS before detection. Then, controlling thebandwidth associated with the WUS based on the reception conditionmetric may comprise controlling a channel selective filter bandwidthbased on the reception condition metric.

In some embodiments, controlling the bandwidth associated with the WUSbased on the reception condition metric may comprise transmitting asignal which is based on the reception condition metric to the accesspoint for controlling a WUS bandwidth. The signal which is based on thereception condition metric may be a WUS bandwidth request.

The wireless communication apparatus may be the access point accordingto some embodiments.

In some embodiments, controlling the bandwidth associated with the WUSbased on the reception condition metric may comprise controlling a WUSbandwidth based on the reception condition metric.

The method may further comprise receiving a signal which is based on thereception condition metric from the wireless communication deviceaccording to some embodiments. The signal which is based on thereception condition metric may be a WUS bandwidth request.

According to some embodiments, receiving the WUS bandwidth request maycomprise receiving two or more respective WUS bandwidth requests fromtwo or more respective wireless communication devices targeted by theWUS. Then, controlling the WUS bandwidth may comprise selecting thewidest bandwidth among the WUS bandwidth requests as the WUS bandwidth.

A second aspect is a computer program product comprising anon-transitory computer readable medium, having thereon a computerprogram comprising program instructions. The computer program isloadable into a data processing unit and configured to cause executionof the method according to the first aspect when the computer program isrun by the data processing unit.

A third aspect is an arrangement for a wireless communication apparatusconfigured to use a wake-up signal (WUS), transmitted, e.g. by an accesspoint, for waking up a main receiver of a wireless communication deviceresponsive to detection of the WUS by a wake-up receiver (WUR) of thewireless communication device.

The arrangement comprises a controller configured to cause control of abandwidth associated with the WUS based on a reception condition metricof the WUR.

A fourth aspect is a wireless communication device comprising thearrangement of the third aspect.

A fifth aspect is an access point comprising the arrangement of thethird aspect.

In some embodiments, any of the above aspects may additionally havefeatures identical with or corresponding to any of the various featuresas explained above for any of the other aspects.

An advantage of some embodiments is that WUS detection may be enabled innon-favorable reception conditions.

This advantage may, for example, be achieved by using a relatively largeWUS bandwidth to enable an increased maximum allowable transmissionpower compared to if a relatively small WUS bandwidth were used. Since amaximum allowable transmission power is typically specified perfrequency unit (e.g. per sub-carrier or per Hz), a larger bandwidthincreases the maximum allowable transmission power. A highertransmission power, in turn, may increase the range for the WUS and,correspondingly, may increase a signal quality metric, e.g.signal-to-interference ratio (SIR), at a WUR receiving the WUS.

Alternatively or additionally, this advantage may, for example, beachieved by using a channel selection filter (CSF) bandwidth in the WURthat has substantially the same bandwidth as the WUS. A larger CSFbandwidth would typically increase the noise at the filter output and,thus, lower the signal quality metric. A smaller CSF bandwidth wouldexclude some of the received WUS power and, thus, lower the signalquality metric.

Another advantage of some embodiments is that WUS reception may beenabled with low power consumption.

This advantage may, for example, be achieved by using a channelselection filter (CSF) bandwidth in the WUR that is relatively small(typically smaller than the bandwidth of the WUS, or having the samebandwidth as the WUS). Using a small bandwidth of the CSF is typicallymore power efficient than using a large bandwidth of the CSF.

Yet an advantage of some embodiments is that a trade-off betweenenabling WUS detection in non-favorable reception conditions and havinglow power consumption in the WUR may be achieved by dynamically adaptingthe WUS bandwidth and/or the CSF bandwidth based on receptionconditions. Typically, relatively wide bandwidth(s) may be used innon-favorable reception conditions to achieve robust WUS detection andrelatively narrow bandwidth(s) may be used in favorable receptionconditions to lower the WUR power consumption.

Some embodiments provide a flexible implementation of wake-up receiversand/or transmitters, which enables improved coverage without using morepower than necessary. Alternatively or additionally, some embodimentsprovide a flexible implementation of wake-up receivers and/ortransmitters, which enables reduced power consumption withoutsacrificing range.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects, features and advantages will appear from the followingdetailed description of embodiments, with reference being made to theaccompanying drawings. The drawings are not necessarily to scale,emphasis instead being placed upon illustrating the example embodiments.

FIG. 1 is flowchart illustrating example method steps according to someembodiments;

FIG. 2 , parts (a) and (b), are plots illustrating example correlationvalues and threshold values according to some embodiments;

FIG. 3 is a combined flowchart and signaling diagram illustratingexample method steps and signaling according to some embodiments;

FIG. 4 is a combined flowchart and signaling diagram illustratingexample method steps and signaling according to some embodiments;

FIG. 5 is a schematic block diagram illustrating an example arrangementcomprising a WUR according to some embodiments;

FIG. 6 is a schematic diagram illustrating an example WUR receptionchain according to some embodiments;

FIGS. 7-9 are schematic block diagrams illustrating example arrangementsaccording to some embodiments;

FIG. 10 is a schematic drawing illustrating an example computer readablemedium according to some embodiments; and

FIG. 11 , parts (a), (b) and (c), are plots illustrating example packeterror rates (PER) as functions of signal-to-noise ratio (SNR) accordingto some embodiments.

DETAILED DESCRIPTION

As already mentioned above, it should be emphasized that the term“comprises/comprising” when used in this specification is taken tospecify the presence of stated features, integers, steps, or components,but does not preclude the presence or addition of one or more otherfeatures, integers, steps, components, or groups thereof. As usedherein, the singular forms “a”, “an” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise.

Embodiments of the present disclosure will be described and exemplifiedmore fully hereinafter with reference to the accompanying drawings. Thesolutions disclosed herein can, however, be realized in many differentforms and should not be construed as being limited to the embodimentsset forth herein.

In the following, embodiments will be described where a bandwidthassociated with the WUS is controlled based on a reception conditionmetric for the WUR. Some general embodiments will be described to startwith. Thereafter, example embodiments will be described with referenceto the drawings. It should be understood that a feature described inconnection to one embodiment (or a group of embodiments) may generallybe applicable also to other embodiments, if suitable.

According to some embodiments, a method is provided for a wirelesscommunication apparatus configured to use a WUS transmitted, e.g. by anaccess point, for waking up a main receiver of a wireless communicationdevice responsive to detection of the WUS by a WUR of the wirelesscommunication device.

According to some embodiments, the wireless communication apparatus maybe a sensor or similar less complex device, and another wirelesscommunication apparatus (a wireless communication device or an accesspoint) can transmit a WUS in order to wake up the sensor. Thus, awireless communication device can act as an “access point node”.Throughout the rest of the description, an access point AP in the usualsense is sending the WUS to the wireless communication apparatus butthis in not to be construed as limiting, and any device acting as anaccess point node and transmitting a WUS is equally applicable.

The method comprises controlling a bandwidth associated with the WUSbased on a reception condition metric for the WUR. In some embodimentsthe method may further comprise determining the reception conditionmetric.

The reception condition metric may be any suitable metric, for example(but not limited to), a received signal strength metric (e.g. RSSI,received signal strength indicator), a path loss, a signal-to-noiseratio (SNR) or similar (e.g. signal-to-interference ratio, SIR). In someembodiments, the reception condition metric may be an extreme (e.g.maximum or minimum) correlation value as will be elaborated on furtherlater herein.

The control of the bandwidth associated with the WUS may, typically,comprise letting a first reception condition value cause the bandwidthto be a first bandwidth and a second reception condition value cause thebandwidth to be a second bandwidth, wherein the first bandwidth is morenarrow than the second bandwidth when the first reception conditionvalue indicates more favorable reception conditions than does the secondreception condition value.

Favorable and non-favorable reception conditions may be defined via thereception condition metric. For example, a relatively high SIR value mayindicate relatively favorable reception conditions and a relatively lowSIR value may indicate relatively non-favorable reception conditions. Ifthe correlation value is used, a relatively high maximum correlationvalue may indicate relatively favorable reception conditions and arelatively low maximum correlation value may indicate relativelynon-favorable reception conditions.

The wireless communication apparatus carrying out the method may be thewireless communication device (WCD, e.g. a station (STA) compatible withoperation in accordance to IEEE 802.11). Alternatively or additionally,the wireless communication apparatus carrying out the method may be theaccess point (AP, e.g. compatible with operation in accordance to IEEE802.11).

In some embodiments, determination of the reception condition metric forthe WUR is performed by the WCD. For example, this may be achieved bycorrelating a received signal comprising the WUS with a WUS referencesignal to provide a maximum correlation value, and determining thereception condition metric for the WUR based on the maximum correlationvalue.

Determining the reception condition metric for the WUR based on themaximum correlation value may, for example, comprise comparing themaximum correlation value to a reception condition threshold value. Whenthe maximum correlation value is higher than the reception conditionthreshold value it may be determined that the reception condition metrichas a first reception condition value. When the maximum correlationvalue is not higher than the reception condition threshold value it maybe determined that the reception condition metric has a second receptioncondition value.

Here, the first reception condition value indicates more favorablereception conditions than does the second reception condition value.Hence, a narrower bandwidth should be applied in relation to the firstreception condition value than in relation to the second receptioncondition value.

Generally, there may be one or more reception condition thresholdscorresponding to two or more intervals of reception condition metricvalues where a certain bandwidth is to be used for each interval.

Also generally, the reception condition threshold value(s) may be staticor dynamic. In a typical example, the reception condition thresholdvalue varies dynamically in relation to a currently applied channelselection filter (CSF) bandwidth of the WUR. A relatively wide CSFbandwidth may be associated with a relatively low reception conditionthreshold value, and vice versa. Put more generally, the receptioncondition threshold value may be dynamically adaptable based on animmediately previous bandwidth associated with the WUS.

The detection of the WUS may comprise comparing the maximum correlationvalue to a WUS detection threshold value which is lower than thereception condition threshold, and waking up the main receiver when themaximum correlation value is larger than the WUS detection thresholdvalue.

According to other embodiments, also a next highest maximum correlationvalue is considered, i.e. a local maximum value. For example, thesynchronization word could be devised such that there is also anotherpeak that is worth considering. Another possibility is to havecomplementary sequences which basically means that the correlation alsowill result in one or more negative peaks, i.e. minimum correlationvalues that may be considered. In other words, global and local extremevalues may be considered for correlation. Similarly to the embodimentsdescribed above, one or more reception condition thresholds may bedefined, corresponding to two or more intervals of reception conditionmetric values to be determined using the further or alternative extremecorrelation values.

Similarly as for the reception condition threshold value, the WUSdetection threshold value may be dynamically adaptable based on animmediately previous bandwidth associated with the WUS. In a typicalexample, the WUS detection threshold value varies dynamically inrelation to a currently applied channel selection filter (CSF) bandwidthof the WUR. A relatively wide CSF bandwidth may be associated with arelatively low reception condition threshold value, and vice versa.Typically, the WUS detection threshold value is lower than thecorresponding reception condition threshold value.

Typically, the same correlation process and maximum correlation value isused for both WUS detection and for control of the bandwidth based onthe reception condition metric.

As already touched upon, the bandwidth associated with the WUS which iscontrolled based on the reception condition metric may be either or bothof a WUS bandwidth and a filter bandwidth of a channel selection filter(CSF) of the WUR. The CSF may be a bandpass filter or a low pass filteras applicable in the relevant WUR implementation.

When the CSF bandwidth is controlled based on the reception conditionmetric, such control may, for example, comprise selecting a CSFbandwidth which is substantially equal to the WUS bandwidth innon-favorable reception conditions and selecting a CSF bandwidth whichis narrower than the WUS bandwidth in favorable reception conditions.

For example, the CSF may be narrower than the WUS bandwidth by a factor.Such a factor may, in some embodiments, be a number between 1 and 8, forexample 2 or 4 or 8. The factor may have different values depending onthe reception conditions, such that the more favorable conditions, thelarger the value of the factor. In some embodiments, the factor may berelated to the symbol rate.

When the WUS bandwidth is controlled based on the reception conditionmetric, such control may, for example, comprise selecting a relativelywide WUS bandwidth in non-favorable reception conditions and selecting arelatively narrow WUS bandwidth in favorable reception conditions.

Various combinations are also possible. For example, a narrow WUSbandwidth may be used together with a CSF bandwidth that issubstantially equal to the WUS bandwidth in very favorable receptionconditions, a wide WUS bandwidth may be used together with a CSFbandwidth that is narrower than the WUS bandwidth in average receptionconditions, and a wide WUS bandwidth may be used together with a CSFbandwidth that is substantially equal to the WUS bandwidth innon-favorable reception conditions.

When the WUS bandwidth is controlled based on the reception conditionmetric, the WCD may transmit a signal which is based on the receptioncondition metric to the access point. The signal may be indicative ofthe reception condition metric (e.g. may comprise the receptioncondition metric). Alternatively, the signal which is based on thereception condition metric may be a WUS bandwidth request (e.g.indicative of a WUS bandwidth suitable for the current receptionconditions of the WCD).

The signal which is based on the reception condition metric may betransmitted to the transmitter of the WUS, e.g. the access point, atregular time intervals or when some relevant event occurs (e.g. a changeof the value of the reception condition metric).

In some embodiments, the WUS bandwidth request may be related to acurrently used CSF bandwidth of the WCD. For example, the WUS bandwidthrequest may indicate a WUS bandwidth which is substantially equal to thecurrently used CSF bandwidth. In such embodiments, the WUS bandwidthrequest may be transmitted to the access point when the CSF bandwidth ofthe WCD is changed.

Generally, a WUS may be directed to a single WUR (unicast) or to aplurality of WUR:s (multicast or broadcast).

In the latter case, the WUS bandwidth may be determined based on thenumber of WUR:s targeted by a WUS. Typically, more targeted WUR:s may berelated to a wider WUS bandwidth, and vice versa. Thus, the number oftargeted WUR:s may be seen as a reception condition metric value, wherea large number of targeted WUR:s corresponds to non-favorable receptionconditions, and vice versa. The reason why the number of targeted WUR:smay be used as a metric is that the reception conditions may beconsidered to be related to the WUR with the worst conditions as thetarget is to be able to reach all WURs.

For example, if the number of targeted WUR:s exceeds a WUR quantitythreshold value a relatively wide WUS bandwidth may be used and if thenumber of targeted WUR:s does not exceed the WUR quantity thresholdvalue a relatively narrow WUS bandwidth may be used. The WUR quantitythreshold value may, for example, be set to one, such that a narrowbandwidth is used for unicast and a wide bandwidth is used for multicastand broadcast.

Several WUR quantity threshold values may be used to define intervals ofWUR quantities, each interval associated with a corresponding WUSbandwidth to be used.

When a WUS is directed to two or more WCD:s and a WUS bandwidth requestis received by each of the two or more WCD:s, the widest WUS bandwidthamong the WUS bandwidth requests may be selected as the WUS bandwidth.

In some embodiments, a WUS (directed to a single WUR or to a pluralityof WUR:s) may be multiplexed in a frequency dimension with other WUS:s.In such embodiments, the WUS bandwidth may be controlled in relation towhether or not the WUS is to be multiplexed, such that a narrowbandwidth is used if the WUS is to be multiplexed. Thus, the number ofseparate WUS:s to be multiplexed for transmission may be seen as areception condition metric value, where a large number of separate WUS:scorresponds to favorable reception conditions, and vice versa.

According to one aspect a method and an arrangement are provided for awireless communication device (WCD). The WCD is configured to use a WUSwhich has a WUS bandwidth, and which is transmitted by e.g. an accesspoint for waking up a main receiver of the WCD responsive to detectionof the WUS by a WUR of the WCD. The WUR comprises a channel selectivefilter for filtering of the WUS before detection and the methodcomprises using a channel selective filter bandwidth that is narrowerthan the WUS bandwidth while the arrangement comprises a controllerconfigured to cause use of a channel selective filter bandwidth that isnarrower than the WUS bandwidth.

An arrangement for either or both of a wireless communication device andan access point is also provided. The apparatus comprising thearrangement is configured to use a WUS transmitted by an access pointfor waking up a main receiver of a wireless communication deviceresponsive to detection of the WUS by a WUR of the wirelesscommunication device.

In some embodiments, the arrangement comprises a controller (e.g.control circuitry) configured to cause execution of the method asdescribed above.

In some embodiments, the arrangement comprises (alternatively oradditionally to the controller) bandwidth control circuitry (e.g. abandwidth controller or a bandwidth control module) configured tocontrol of a bandwidth associated with the WUS based on a receptioncondition metric of the WUR as has been described above.

In some embodiments, the arrangement comprises (alternatively oradditionally to the controller) determination circuitry (e.g. adeterminer or a determination module) configured to determine thereception condition metric of the WUR as has been described above.

FIG. 1 schematically illustrates an example method 100 according to someembodiments. The method may be for a wireless communication apparatus(WCD or AP) configured to use a WUS transmitted by an access point forwaking up a main receiver of a wireless communication device responsiveto detection of the WUS by a WUR of the wireless communication device.

The method starts in optional step 110, where a reception conditionmetric for the WUR is determined. In step 120, a bandwidth associatedwith the WUS is controlled based on the reception condition metric forthe WUR as explained herein.

FIG. 2 are plots illustrating example correlation values (correlatoroutput, correlator metric), including maximum correlation values 205,206. The plots also illustrate example WUS detection threshold values(detection threshold) 202, 204 and example reception condition thresholdvalues (relaxed/demanding conditions threshold) 201, 203.

Part (a) exemplifies a situation where a wide CSF is used and part (b)exemplifies a situation where a narrow CSF is used. As mentioned above,the WUS detection threshold values 202 and 204 are typically differentsince different CSF bandwidths are used in the two situations. The sameapplies to the reception condition threshold values 201 and 203

In part (a), when the maximum correlation value 205 is above the WUSdetection threshold 202 the WUS is detected.

Furthermore, when the maximum correlation value 205 is also above thereception condition threshold 201, it may be assumed that the receptionconditions are favorable (relaxed). The CSF may be switched to a narrowbandwidth to lower power consumption and/or a request for narrow WUSbandwidth may be transmitted.

However, when the maximum correlation value 205 is above the WUSdetection threshold 202 but below the reception condition threshold 201,it may be assumed that the reception conditions are non-favorable(demanding) and the CSF may continue to be based on the wide bandwidth.

In part (b), when the maximum correlation value 206 is above the WUSdetection threshold 204 the WUS is detected.

Furthermore, when the maximum correlation value 206 is also above thereception condition threshold 203, it may be assumed that the receptionconditions are favorable (relaxed) and the CSF may continue to be basedon the narrow bandwidth to keep power consumption at a low level.

However, when the maximum correlation value 206 is above the WUSdetection threshold 204 but below the reception condition threshold 203,it may be assumed that the reception conditions are non-favorable(demanding). The CSF may be switched to a wide bandwidth and/or arequest for wide WUS bandwidth may be transmitted.

FIGS. 3 and 4 are combined flowcharts and signaling diagramsillustrating example method steps and signaling when the wirelesscommunication apparatus referred to in connection with FIG. 1 is a WCD(FIG. 3 ) and an AP (FIG. 4 ) and the extreme values are maximumcorrelation values.

In FIG. 3 , an AP 350 transmits a WUS 391 in step 361 and the WUS isreceived by the WCD 300 in step 301.

In step 310, the WCD determines the reception condition metric for theWUR by correlating the received signal comprising the WUS with a WUSreference signal to provide a maximum correlation value (illustrated bysub-step 311) and determining the reception condition metric for the WURbased on the maximum correlation value (illustrated by sub-step 312).For example, sub-step 312 may comprise comparing the maximum correlationvalue to a reception condition threshold value and determining thereception condition metric to have a first or second reception conditionvalue depending on whether or not the maximum correlation value ishigher than the reception condition threshold value (compare with theprocedure described in connection to FIG. 2 , for example).

In step 320, the WCD controls a bandwidth associated with the WUS basedon the reception condition metric. The bandwidth associated with the WUSmay be the bandwidth of a CSF of the WUR (illustrated by sub-step 321)and/or may be a WUS bandwidth. In the latter case, the WCD may transmita WUS bandwidth request 392 to the AP as illustrated by sub-step 322.The WUS bandwidth request is received by the AP in step 372 and the APmay control the WUS bandwidth of an upcoming WUS transmission based onthe received request (illustrated by step 373).

The WCD may also compare the maximum correlation value to a WUSdetection threshold value (illustrated by step 330) and wake up the mainreceiver when the maximum correlation value is larger than the WUSdetection threshold value (illustrated by step 340). Even though steps330 and 340 have been illustrated in FIG. 3 to be performed after steps310 and 320, these steps may be performed in any order or partly orfully in parallel, as applicable. For example, steps 330 and 340 may beperformed after sub-step 311 and before or in parallel to (sub-)steps312 and 320.

In FIG. 4 , a WCD 400 transmits a WUS bandwidth request 492 in step 401and the WUS bandwidth request is received by the AP 450 in step 411.Alternatively or additionally, the AP 450 may determine the number ofWCD:s targeted by a WUS to be transmitted as illustrated by step 412.Yet alternatively or additionally, the AP 450 may determine if the WUSto be transmitted is to be multiplexed in a frequency domain asillustrated by step 413.

In step 420, the AP controls a bandwidth associated with the WUS basedon the reception condition metric. The bandwidth associated with the WUSmay be a WUS bandwidth as indicated in step 420. Numerous variations ofthe determination of step 420 may be envisioned and a few examples aregiven in the following.

If a single WCD is targeted by a WUS and a WUS request has been receivedfrom that WCD, the AP may select the WUS bandwidth requested. If severalWCD:s are targeted by a WUS, the AP may select the widest possible WUSbandwidth to accommodate different conditions for the different WCD:s(illustrated by sub-step 422). If several WCD:s are targeted by a WUSand a WUS request has been received from the WCD:s, the AP may selectthe widest WUS bandwidth among those requested (illustrated by sub-step421). If the WUS is to be multiplexed before transmission, the AP mayselect a narrow bandwidth to enable the multiplexing (illustrated bysub-step 423).

After the control of the WUS bandwidth in step 420, the WUS 491 istransmitted accordingly in step 461 and received by the WCD in step 402.

FIG. 5 schematically illustrates an example arrangement 500 comprising aWUR 501 and a main receiver (MR) 501.

In a low power mode, the main receiver 502 is turned off (or set tosleep mode, or similar) and the switch 503 is set to the position shownin FIG. 5 . When the WUR detects a WUS, it causes a change of theposition of the switch (illustrated by control signal 504) and a wake-upof the main receiver (illustrated by control signal 505).

It should be understood that other implementations using a WUR may beequally applicable in the context presented herein, and that thestructure of FIG. 5 is merely provided as an example. For example, theswitch 503 may be replaced by circuitry providing a similar function orthere may be one antenna for the WUR and one for the main receiver(rendering the switch unnecessary).

FIG. 6 schematically illustrates an example WUR reception chain 600according to some embodiments. The WUR reception chain comprises a lownoise amplifier (LNA) 601 and a mixer 602 for mixing the output of theLNA with a local oscillator (LO) signal 603. The output of the mixer isprovided to a channel selection filter (CSF) 605 after having passed afurther amplifier 604, and the filtered signal is input to an envelopedetector 606. At the output of the envelope detector, there is providedan analog-to-digital converter (ADC) 607 and a correlator (CORR) 608.

FIGS. 7-9 are schematic block diagrams illustrating example arrangementsaccording to some embodiments as described herein.

FIG. 7 is a generic arrangement comprising a controller (CNTR; controlcircuitry or control module) 700 for a wireless communication apparatus.The controller may be adapted to cause execution of any of the methodsdescribed herein, for example, the methods of any of FIGS. 1, 3 and 4 .The arrangement of FIG. 7 may comprise a determiner (DET; determinationcircuitry or determination module) 701 for determining the receptioncondition metric and/or a bandwidth controller (BWC; bandwidth controlcircuitry or bandwidth control module) 702 for controlling the bandwidthassociated with the WUS based on the reception condition metric. Thedeterminer and/or the bandwidth controller may be comprised in, orotherwise associated with, the controller 700.

FIG. 8 is an arrangement for a WCD comprising a controller (CNTR;control circuitry or control module) 800. The controller may be adaptedto cause execution of any of the methods described herein for WCD:s, forexample, the methods of any of FIGS. 1 and 3 . The arrangement of FIG. 8may comprise a determiner (DET; determination circuitry or determinationmodule) 801 for determining the reception condition metric and/or abandwidth controller (BWC; bandwidth control circuitry or bandwidthcontrol module) 802 for controlling the bandwidth associated with theWUS based on the reception condition metric. The determiner and/or thebandwidth controller may be comprised in, or otherwise associated with,the controller 800. The arrangement may also comprise a WUR 810 having aCSF 815. The controller 800 may be comprised in, or otherwise associatedwith, the WUR 810. The arrangement may also comprise a transceiver(TX/RX; transceiving circuitry or transceiving module) 812 fortransmission of a WUS bandwidth request. The transceiver 812 may, forexample, be the main receiver.

FIG. 9 is an arrangement for an AP comprising a controller (CNTR;control circuitry or control module) 900. The controller may be adaptedto cause execution of any of the methods described herein for AP:s, forexample, the methods of any of FIGS. 1 and 4 . The arrangement of FIG. 9may comprise a determiner (DET; determination circuitry or determinationmodule) 901 for determining the reception condition metric and/or abandwidth controller (BWC; bandwidth control circuitry or bandwidthcontrol module) 902 for controlling the bandwidth associated with theWUS based on the reception condition metric. The determiner and/or thebandwidth controller may be comprised in, or otherwise associated with,the controller 900. The arrangement may also comprise a scheduler (SCH;scheduling circuitry or scheduling module) 913 for allocatingtransmission resources to the WUS (which transmission resources arebased on the WUS bandwidth). The arrangement may also comprise atransceiver (TX/RX; transceiving circuitry or transceiving module) 912for transmission of the WUS.

The described embodiments and their equivalents may be realized insoftware or hardware or a combination thereof. The embodiments may beperformed by general purpose circuitry. Examples of general purposecircuitry include digital signal processors (DSP), central processingunits (CPU), co-processor units, field programmable gate arrays (FPGA)and other programmable hardware. Alternatively or additionally, theembodiments may be performed by specialized circuitry, such asapplication specific integrated circuits (ASIC). The general purposecircuitry and/or the specialized circuitry may, for example, beassociated with or comprised in an apparatus such as a wirelesscommunication device or an access point.

Embodiments may appear within an electronic apparatus (such as awireless communication device or an access point) comprisingarrangements, circuitry, and/or logic according to any of theembodiments described herein. Alternatively or additionally, anelectronic apparatus (such as a wireless communication device or anaccess point) may be configured to perform methods according to any ofthe embodiments described herein.

According to some embodiments, a computer program product comprises acomputer readable medium such as, for example a universal serial bus(USB) memory, a plug-in card, an embedded drive or a read only memory(ROM). FIG. 10 illustrates an example computer readable medium in theform of a compact disc (CD) ROM 1000. The computer readable medium hasstored thereon a computer program comprising program instructions. Thecomputer program is loadable into a data processor (PROC) 1020, whichmay, for example, be comprised in a wireless communication device or anaccess point 1010. When loaded into the data processing unit, thecomputer program may be stored in a memory (MEM) 1030 associated with orcomprised in the data-processing unit. According to some embodiments,the computer program may, when loaded into and run by the dataprocessing unit, cause execution of method steps according to, forexample, any of the methods illustrated in FIGS. 1, 3 and 4 .

Thus, to achieve low power consumption in the WUR, it is desirable touse a channel selective filter with a relatively small bandwidth (andalso of low order if possible). Generally, a filter with relativelynarrow bandwidth is easier realized as a low order filter than is afilter with relatively wide bandwidth, if the same or similarattenuation is to be achieved outside the signal bandwidth of the WUS.In some scenarios, the power consumption may be proportional to theorder of the filter. Thus, lowering the power consumption of the WUR,may be achieved by using a relatively narrow filter bandwidth whichenables use of a relatively low order implementation. For example, ifadjacent channel interference is to be suppressed (say at a distance of10 MHz), then a 2 MHz filter may be implemented as having a lower orderthan a 8 MHz filter. However, also in case the same order filters wouldbe applied, which may simplify switching between different bandwidths,it may be advantageous from a power consumption perspective to use afilter of narrower bandwidth.

On the other hand, due to regulatory requirements the maximumtransmission power that can be used is often limited by the powerspectrum density (PSD). This limitation means that, although a hightotal transmission power may be allowed, it cannot be used if thebandwidth of the signal is too small.

Since a reduced transmission power means that the range of the WUS willbe reduced, the above results in a trade-off between receiver powerconsumption and transmission range. Therefore, some embodiments providea method and an apparatus for flexible signaling and/or reception of aWUS. This will now be even further exemplified.

The bandwidth of the transmitted WUS can be adapted based on rangerequirements such that a wider signal bandwidth may be used when therequirements are harder, i.e., the path loss from the transmitter to theWUR is higher. Alternatively or additionally, a wider bandwidth may beused for the WUS whether needed or not, and the WUR can autonomouslydecide what bandwidth to use in a CSF in order to minimize its powerconsumption. The latter is particularly suitable when the WUS isintended for two or more WUR:s, i.e., when the WUS is a multicast orbroadcast message.

Of course, the specific system with its specific parameters used hereinto exemplify various embodiments is not meant as limiting to. As obviousto those with skill in the art, the examples presented herein are easilyadopted to other systems with potentially very different parameters.Suppose that the considered system is based on IEEE 802.11, and supposethat the channel bandwidth used is 20 MHz. Assuming now that the wake-upsignal used for the WUR is 4 MHz and comparing this with thetransmission of the regular 802.11 transmission it can be seen thatthere is a significant penalty in terms of the allowed transmissionpower that can be used for the wake-up signal. This is described indetail in S. Shellhammer and B. Tian, “Regulations and noisefigure—Impact on SNR”, IEEE 802.11-17/0365r0, and some key points arejust repeated here. For the 2.4 GHz band, the European regulationslimits the maximum transmission power of the 4 MHz WUS to be 16 dBmbased on the power spectrum density limit of 10 dBm/MHz, whereas at thesame time the regular IEEE 802.11 transmission may be 20 dBm. In the 5GHz band the corresponding difference in maximum allowed transmissionpower will be 7 dB in Europe, US, and China.

Taking into account that the WUR is assumed to be very power efficient,it is (in Shellhammer and Tian, “Data Rates and Coding”, IEEE802.11-17/0670r0) argued that it can be expected that the noise figure(NF) for the WUR is about 8 dB higher than for the regular receiver.Consequently, considering the link-budget for the WUR and the regulartransceiver, there may be as much as 15 dB difference between the twosystems.

To understand some embodiments more easily, it is helpful to consider arather generic WUR architecture as illustrated in FIG. 6 . The receivedsignal is amplified in a low noise amplifier (LNA) 601 and thendown-converted by the mixer 602 from the radio frequency (e.g. around2.4 GHz) to—for example—an intermediate frequency (IF) at, say, 10 MHz.The IF signal may then be further amplified in 604 and filtered througha channel selection filter (here; a bandpass filter—BPF—centered aroundIF). In a standard receiver, the bandwidth of the BPF is approximatelyequal to the bandwidth of the desired signal such that potentiallyinterfering signals in adjacent channels are attenuated by the BPF.However, to allow for a bandwidth of the BPF that is roughly the same asthe bandwidth of the desired signal, is required that the frequencygenerated by the local-oscillator (LO) is very accurate, becauseotherwise there is a risk that a non-negligible part of the energy ofthe WUS will be filtered out, which negatively impacts the performanceof the WUR. Embodiments presented herein are applicable irrespectivelyof whether the bandwidth of the BPF is matched to the bandwidth of theWUS or if a BPF of much larger bandwidth is used.

As will be seen, there is a substantial gain in either case, althoughthe gain decreases the narrower the BPF can be made. Using a widersignal gives a gain because you can use higher transmit (TX) power. Ifthe BPF is not changed the gain is identical to the increase in TXpower. If a narrower filter is used for a narrower signal, this improvesthe performance for the narrow signal since the noise power that entersthe detector will be reduced. However, in the context with an envelopedetector herein, it turns out that reducing the filter bandwidth doesnot fully compensate for the increased TX power. The gain is decreasedif using a large TX bandwidth, but there is still a gain.

After the BPF 605 of FIG. 6 , the signal is demodulated using anenvelope detector 606, converted to a digital stream by means of ananalog-to-digital converter (ADC) 607, and then processed digitally.Typically, the digital processing involves e.g. time estimation by meansof correlation of the received signal with a known synchronizationsequence in a correlator 608.

Although the architecture illustrated in FIG. 6 is largely operating inthe analog domain, e.g. the envelope detector is before the ADC, it ispossible to instead perform a larger part of the receiver processing inthe digital domain. For example, additional filtering and the envelopedetector may be implemented in the digital domain according to someembodiments.

One reason for selecting a relatively narrow bandwidth for the BPF isthat it may allow for lower power consumption, which is typically one ofthe key parameters for a WUR. Another reason for selecting a relativelynarrow bandwidth of the WUS is that it can easily fit in a 20 MHzchannel and can be more easily protected from interference from adjacent20 MHz channels since the BPF will have a narrow passband andconsequently a large frequency distance to the adjacent channel.

When selecting the bandwidth of a transmitted signal, this is typicallybased on what data rate is to be supported. The higher the data rate,the wider the bandwidth. In case of a WUS, this is not the case. Anattractive means to generate the WUS was presented in M. Park et al.“Low-power wake-up receiver (LP-WUR) for 802.11,” IEEE 802.11-15/1307r1.An attractive modulation to be used for the WUS in on-off keying (OOK)as this allows for a very simple receiver based on an envelope detector(compare with FIG. 6 ). In Park et al., it was proposed to generate theOOK signal by using the same inverse fast Fourier transform (IFFT) blockas is used for transmitting the regular IEEE 802.11 signal. ON was thenrepresented by populating 13 sub-carriers by some signal, whereas OFFwas represented by not sending anything. The IFFT block is using a 64point FFT and is clocked at 20 MHz, which results in that thetransmitted signal (in case of ON) will have a bandwidth ofapproximately 13×312.5 kHz=4 MHz, since the sub-carrier spacing in 20MHz/64=312.5 kHz.

Since the WUS is generated using a 64 point FFT at 20 MHz samplingfrequency, the duration of one OFDM symbol is 3.2 μs. If a cyclic prefix(CP) of 0.8 μs is added, which is commonplace in IEEE 802.11, the totalduration of an OFDM symbol including the CP is 4 μs and thecorresponding symbol rate thus becomes 250 ksymbols/s (equivalent to 250kb/s for WUS). If the WUS is generated using 52 sub-carriers instead,i.e., four times more carriers, the symbol rate remains the same, i.e.,250 ksymbols/s (equivalent to 250 kb/s for WUS).

A comparison may be made of how the performance of a WUR depends on thebandwidth of the WUS. The working procedure of the receiver in FIG. 6 isactually independent of the bandwidth of the signal, the only (possible)exception being the CSF 605 in front of the envelope detector.

FIG. 11 illustrates resulting packet error rates (PER) of somesimulations performed to evaluate the impact of the bandwidth of theWUS. The WUS is generated using a 64 point FFT and adding a CP asdescribed above. Manchester coding is applied, i.e., a logical zero isrepresented by transmitting one symbol being OFF followed by one symbolbeing ON, whereas a logical one is represented by transmitting onesymbol being ON followed by one symbol being OFF. The use of Manchestercoding reduced the effective data rate to 125 kb/s. This will improvethe performance in terms of sensitivity, but the main reason forapplying Manchester coding, however, is that it considerably simplifythe demodulation of the signal. Specifically, if plain OOK is employed,a decision threshold needs to be estimated which is to be used to decidewhether the received signal corresponds to ON or OFF. With Manchestercoding, there is no need for a threshold, but instead the decision isbased on comparing the first symbol with the last, and deciding in favorof a logical zero if the first OOK symbol contains less energy than thesecond and decide in favor of a logical one if the first OOK symbolcontains more energy than the second one.

The simulated performance when no (or a very wide) BPF is used isdepicted in part (a) of FIG. 11 . The SNR is defined as the power of thedesired signal divided by the power of the noise after the mixer andbefore the CSF. As can be seen the performance of the WUR is basicallyindependent of the bandwidth of the WUS in this case. The reason for nothaving a CSF at all, or using a CSF with a bandwidth that is much largerthan the bandwidth of the actual WUS, is that it allows for a veryrelaxed implementation of the frequency generation circuitry (LO).

Since the required SNR is the same irrespective of the bandwidth of theWUS, but the allowed transmission power is proportional to the usedbandwidth, the path loss that can be handled in case a larger bandwidthis used will be correspondingly increased. As a simple example toappreciate this, consider a link budget calculation where the maximumpath loss, PL, that can be accepted is given by (in dB):PL=P _(TX) −RX _(sens)[dB],where RX_(sens) is the sensitivity of the WUR and P_(TX) is thetransmission power. RX_(sens) can then be calculated as:RX _(sens) =kTB+NF+SNR=−101+15+(−3)=−89dBm.

Here, kTB is the thermal noise floor calculated for a bandwidth of 20MHz, NF is the noise figure which is assumed to be 15 dB (followingShellhammer and Tian this is assumed a reasonable value taken to be 8 dBhigher than for the regular IEEE 802.11 receiver), and −3 dB is therequired SNR to obtain a frame error rate of less than 10%, which isobtained from FIG. 11 , part (a).

Next, to relate this to coverage, the path loss, e.g. at 5.5 GHz, ismodelled as function of the distance, d, as followsPL=47+3.5 log₁₀ d[dB].

Here, the term 47 corresponds to free space path loss for 1 meter at5.5. GHz, and the distance d is in meters. The factor 3.5 is often usedto model how the path loss depends on distance (d^(3.5)). In the case offree space, 2.0 might be used instead. From Shellhammer and Tian weobtain that the maximum transmission power is limited by the PSD to 10dBm/MHz in 5 GHz.

For the two WUS signals using 13 and 52 sub-carriers, respectively, themaximum transmission power therefore becomes 16 and 22 dBm,respectively. This, in turn, corresponds to a maximum path loss of16−(−89)=105 dB and 22−(−89)=111 dB, respectively. Converting this tocoverage, it is readily calculated that the corresponding range is 45and 67 meters, i.e., by increasing the bandwidth of the WUS the rangehas been increased by roughly 50%. Similar derivations can be made forthe 2.4 GHz band and others.

In case one would find it beneficial to implement a CSF with a bandwidthcorresponding to the bandwidth of the WUS, the sensitivity performancewill be somewhat improved. In FIG. 11 , part (b), the correspondingsimulated performance is shown, but now with a CSF with a bandwidth thatis the same as the signal bandwidth of the WUS. As can be seen, theperformance is improved for the signal with the smaller bandwidth tosome extent. Specifically the 4 MHz signal (13 sub-carriers) now has arequired SNR of about −6 dB, whereas the 16 MHz signal (52 sub-carriers)has a required sensitivity of about −4 dB, implying at 2 dB gain for thenarrower signal.

The conclusion is that although the SNR at the input to the envelopedetector can be greatly improved, it does not improve the overallperformance correspondingly. The reason for this is the low pass filter(LPF) which is part of the envelope detector. Although the widebandnoise is input to the nonlinear envelope detector, the LPF stillsuppress the high frequency components to a large extent.

Part (c) of FIG. 11 illustrates the curves of part (b) but where the SNRhas been normalized to illustrate dependency on relative sensitivity.That is, in part (c) the sensitivity performance curves shown in (b)have been scaled taking the maximum allowed transmission power intoaccount. Specifically, assuming that the allowed transmission power isPSD limited, a signal with twice the bandwidth is shifted 3 dB to theleft. Taking curves 1111 and 1113 in Part (b) as examples, the receiverperformance is about 2 dB better for the narrower signal (1113 whichcorresponds to a WUS bandwidth of 4 MHz) than for the wider signal (1111which corresponds to a WUS bandwidth of 16 MHz). However, since the 16MHz signal is four times wider than the 4 MHz signal, it can betransmitted at 6 dB higher power yielding an advantage of 4 dB (i.e. 6−2dB) in terms of link budget. This gain of 4 dB is illustrated byshifting the curve 1111 in part (b) 6 dB to the left for part (c),resulting in the shifted version denoted 1121.

With reference to FIG. 11 , a further example of how the CSF bandwidthmay be selected in relation to the WUS bandwidth may be given. In thesimulations, The bandwidth of the WUS can be 4, 8 or 16 MHz(corresponding to 13, 26 or 52 sub-carriers). The different bandwidthsof the CSF can then be selected to be e.g. 4, 8 and 16 MHz. An examplewhere the bandwidth of the CSF is considerably smaller than the WUSbandwidth would be when the CSF bandwidth is 4 MHz and the WUS bandwidthis 16 MHz, i.e. the factor referred to above would equal 4.

Although the derivations have been based on a super-heterodyne receiverand band-pass filter (FIG. 6 ), the principles are equally applicable toa homodyne (zero-IF) receiver with low-pass filters. Also, low-IFreceivers with low-pass filters or complex band-pass filters can be usedto realize the concept.

Example 1: WUR with Varying Receiver Filter Bandwidth

A WUR receiver is disclosed characterized by that the bandwidth of thechannel selective filter can be varied such that a narrower filter maybe used when the receiver conditions are less demanding whereas a widerfilter may be used when the receiver conditions are more demanding. Forexample, a demanding condition occurs when the WUR is located at theedge of the coverage area. The WUR can determine whether it is in ademanding condition by means of a correlation metric obtained from thecross-correlation of the received signal with a reference signal. Anillustration is given in FIG. 2 , part (a), where the correlation metricis shown, together with two thresholds. In this figure the WUR uses awide CSF. A first threshold 202 is used for WUS detection. A secondthreshold 201, higher than the second, is used to determine whether theconditions are not too demanding and the CSF may be switched to a narrowCSF. Another illustration is given in FIG. 2 , part (b). In this casethe WUR is using a narrow CSF. A WUS is detected when the correlationmetric exceeds a third threshold 204. However, if the correlation metricdoes not exceed a fourth threshold 203 (larger than the thirdthreshold), then the conditions are demanding and a switch to a wide CSFis indicated.

FIG. 2 , part (a) is an illustration of a determination of relaxedconditions at the WUR. In this example, the WUR utilizes a wide CSF.Since the correlation metric 205 exceeds the WUS detection threshold202, a WUS is detected. Moreover since the correlation metric 205 alsoexceeds a relaxed conditions threshold 201, the WUR may switch to anarrow CSF in order to decrease power consumption.

FIG. 2 , part (b) is an illustration of a determination of demandingconditions at the WUR. In this example, the WUR utilizes a narrow CSF.Since the correlation metric 206 exceeds the WUS detection threshold204, a WUS is detected. However since the correlation metric 206 doesnot exceed a demanding conditions threshold 203, the WUR should switchto a wide CSF in order to ensure good receiver performance.

Example 2: Signaling for Request of Signal Bandwidth of the WUS

A method for signaling a request for a WUS bandwidth is disclosed. Themethod characterized by that the device having a WUR sends a request tothe device transmitting the WUS requesting the transmitting device touse a specific bandwidth, out of at least two possible bandwidths, wherethe requested bandwidth may be the same as is already used, or thebandwidth may be smaller than the bandwidth currently used, or thebandwidth may be larger than the bandwidth currently used.

Example 3: Determination of Signal Bandwidth of the WUS Based onFeedback

The bandwidth to be allocated to the WUS is determined by thetransmitter based on feedback from at least one device having a WUR. Thedetermination may be based on feedback from a single device as describedin Example 2, or it can be based on taking feedback from two or moredevices into account. For example, in case the determination is based onfeedback from two or more devices, the decision can be to use thelargest of the bandwidth requested by the different devices providingfeedback.

Example 4: Determination of Signal Bandwidth of the WUS without Feedback

The bandwidth to be used for specific WUS is determined by thetransmitter of the WUS autonomously, i.e., without any feedback from thepotential receivers of the WUS.

For example, the bandwidth may be determined based on the type oftransmission as follows. If the transmission is for a single WUR asmaller bandwidth may be allocated, whereas if the transmission isintended for two or more WUR:s (i.e., the transmission is a multi-castor broadcast transmission) a larger bandwidth may be allocated to theWUS. The rationale for this is that whether a transmission intended fora single device is successful is more easily determined than whether abroadcast transmission is correctly received by all targeted WUR:s.

Alternatively or additionally, if two or more WUS are to be multiplexedin frequency, i.e., using frequency division multiplexing (FDM), thismay only be possible if a more narrow bandwidth would be used for (each)WUS. Therefore the bandwidth of the WUS may be determined based onwhether the transmission of the WUS consists of one WUS, in which case alarger bandwidth may be used, or if the transmission consists of two ormore WUS:s, in which case a smaller bandwidth may be used.

Further Exemplifying:

Variable signal bandwidth of WUS for enhanced performance.

Further details regarding this exemplification may be found in thepresentation material athttps://mentor.ieee.org/802.11/dcn/17/11-17-0662-00-00ba-simulated-wur-performance-in-frequency-selective-channels.pptx.

In Shellhammer and Tian it is high-lighted that a 4 MHz wake-up signalwill suffer about 7 dB in allowed TX power, when the limit is set byPSD. From a power consumption point of view, it is beneficial to havesmaller bandwidth; however the loss in link budget is huge. Oneproposition is to allow the wake-up signal to be sent with a suitablebandwidth which can be used to obtain a (preferably optimum)sensitivity-power consumption trade-off. The WUR can select bandwidth ofthe channel selective filter independent of the signal bandwidth. Thisapproach can be seen as a special case of what was presented in L.Wilhelmsson and M. Lopez, “Concurrent transmission of data and a wake-upsignal in 802.11ax,” IEEE 802.11-17/0094r1, but without concurrenttransmission of data.

A recap of link budget considerations: In Shellhammer and Tian, it isemphasized that a 4 MHz WUS will suffer 4 or 7 dB in allowed TX powerdue to regulatory requirements (different for different bands). It hasalso been agreed that it is reasonable to assume that the noise figureis 8 dB higher for the WUR. In addition, it was shown in L. Wilhelmsson,“Simulated WUR performance in frequency selective channels,” IEEE802.11-17/0662r0, that the loss in frequency diversity for a 4 MHzsignal compared to a 20 MHz channel easily can be a few dB.

Motivation: To compensate for the relatively small bandwidth, the datarate has to be reduced, leading to increased longer wake-up packets, andto some extent leading to increased complexity (harder synchronizationand forward error correction—FEC—decoding). It is proposed to insteadincrease the bandwidth of the signal when needed. That means acorresponding increase in range, but with no cost in power consumptionas the large bandwidth is only used when needed.

Model for receiver processing: See FIG. 6 . The envelope detector 606may comprise a rectifier (as shown) and a low pass filter. The output ofthe ADC 607 may be input to a correlator 608 and the output of thecorrelator may be subtracted from the output of the ADC. Then, theresult may be down-sampled by 4 based on the correlator result. The ADCruns at 4 x oversampling relative WUS symbol rate. The correlator(coefficients +/−1) is operating on signal with DC bias. Manchestercoding is used, so no need to estimate the decision threshold DC.

Varying the signal bandwidth: The WUS bandwidth may be varied, forexample, between 4 MHz, 8 MHz and 16 MHz. The power of the WUS isboosted by allocating more sub-carriers to the WUS. The smallest BWcorresponds to the 13 sub-carriers first proposed in M. Park et al.,“Low-power wake-up receiver (LP-WUR) for 802.11,” IEEE 802.11-15/1307r1.

Simulated sensitivity as a function of signal bandwidth: Simulationset-up as described in connection with FIG. 11 . Performance in AWGN(additive white Gaussian noise) channel without CSF is illustrated inFIG. 11 , part (a). If no channel selective filter (CSF) is used, thebandwidth of the signal should not matter in terms of required SNR.There will be a corresponding gain in the link budget due to theincreased allowed TX power. Performance in AWGN channel with CSF isillustrated in FIG. 11 , parts (b) and (c). With a CSF, a smaller signalbandwidth will also allow for correspondingly less noise at the envelopedetector input. The gain is about 1 dB for a 2× increase of thebandwidth. Consequently, as can be seen in FIG. 11 , part (c), there isa 2 dB gain in terms of link budget for every 2× increase in bandwidth.

Increasing the (noise) bandwidth of the filter in beneficial conditionsis due to the low pass filter (LPF) in the envelope detector. Thebandwidth of the LPF is not determined by the signal bandwidth but bythe data rate, and is 150 kHz here. The LPF still removes part of thenoise power, although the signal is passed through a non-linearcomponent.

WUR implementation aspects and relation to FDM transmission of wake-upsignals: Changing the bandwidth of an analog filter (keeping all otherparameters the same) is easily done by shifting in/out components. Thereare no issues related to switching time. If a wideband WUS is used, aWUR with good channel conditions may still use a CSF with a smallbandwidth in order to save power. For multicast/broadcast, receivers candecide autonomously what filter bandwidth to use if WUS is transmittedwith a large bandwidth. Transmission of several WUS:s may be allowed bymeans of FDM (e.g. three 4 MHz WUS distributed over a frequency range of16 MHz). The approaches herein may, potentially, be seen as ageneralization of the FDM approach to WUS transmission, with a varyingbandwidth.

CSF Implementation Examples:

1) For single user transmissions using the central 4 MHz channel: A2^(nd) order Butterworth filter may be defined. This meets the powerbudget of 40 μW for the filter, accompanied by ˜40 μW of a ringoscillator for which a phase noise model may be provided. This can beused to report performance results for approximately 100-200 μW WUR.

2) For transmissions using the non-central 4 MHz channel: A 5^(th) orderfilter may be defined. The phase noise model may be used again but thenoise profile may be obtained from a higher power consuming LO. Thiscombination may be used to evaluate advanced multi-TX features at theexpense of higher power consumption.

SOME FURTHER EXAMPLE EMBODIMENTS

-   -   1. A wireless terminal (STA) comprising a wake-up receiver (WUR)        with an adaptable filter (BPF/CSF), configured to:        -   adapt the bandwidth of the filter depending on a metric            associated with the reception conditions at the STA (with a            view to minimize the power consumption).    -   2. A wireless terminal as in 1, configured to set the filter to        a relatively narrower bandwidth in good reception conditions,        and to a relatively wider bandwidth in poor reception        conditions.    -   3. A wireless terminal as in 1 or 2, configured to switch the        filter to a narrower bandwidth if the metric falls above a        switching threshold, and configured to switch the filter to a        wider bandwidth if the metric falls below a switching threshold,        wherein the switching thresholds may be the same or different.    -   4. A wireless terminal as in 1-3, wherein the metric is a        correlation metric obtained from the cross-correlation of the        received signal with a reference signal.    -   5. A wireless terminal as in 1-4, configured to set a wake-up        signal (WUS) detection threshold in dependence of the current        bandwidth of the filter. (Put differently; suppose the wider        filter gives better quality of the received signal. Then, maybe        the threshold is the same but the wide bandwidth is needed to        actually declare the WUS as detected, but the threshold as such        is not really changed.)    -   6. A wireless terminal as in 5, wherein the respective detection        thresholds are lower than the respective switching thresholds.    -   7. A wireless terminal as in 1-6, configured to send a request        to an access point (AP) for a desired bandwidth of the wake-up        signal.    -   8. A wireless terminal as in 7, wherein the desired bandwidth of        the wake-up signal is depending on the bandwidth of the filter,        preferably a bandwidth corresponding to the bandwidth of the        filter (thus the sensitivity performance will be somewhat        improved).    -   9. A wireless terminal as in 7-8, configured to send the        bandwidth request at a change of the bandwidth of the filter.    -   10. A wireless terminal (STA) comprising a wake-up receiver        (WUR) with an adaptable bandpass filter (BPF/CSF), configured        to:        -   adapt the bandwidth of the filter depending on a received            wake-up signal, the bandwidth corresponding to the bandwidth            of the WUS (thus the sensitivity performance will be            somewhat improved).    -   11. An access point (AP) configured to send a wake-up signal to        one or more wireless terminals, and further configured to:        -   adapt the bandwidth of the wake-up signal to signaling            conditions between the access point and the wireless            terminal.    -   12. An access point as in 11, configured to use a relatively        wider bandwidth and/or relatively higher transmission power        (density) at a relatively higher path loss between the access        point and the wireless terminal, and to use a relatively        narrower bandwidth and/or relatively lower transmission power        (density) at a relatively lower path loss between the access        point and the wireless terminal.    -   13. An access point as in 11-12, configured to determine the        signaling conditions based on feedback from one or more wireless        terminals.    -   14. An access point as in 13, configured to use the widest        bandwidth requested by a wireless terminal.    -   15. An access point as in 11-14, configured to determine the        signaling conditions based on the number of wireless terminals        targeted to receive the wake-up signal.    -   16. An access point as in 15, configured to use a relatively        narrower bandwidth if a single wireless terminal is targeted to        receive the wake-up signal, and a relatively wider bandwidth if        a several wireless terminals are targeted to receive the wake-up        signal.    -   17. An access point as in 11-16, configured to determine the        signaling conditions based on the number of separate wake-up        signals to be transmitted to one or more wireless terminals.    -   18. An access point as in 17, configured to use a relatively        wider bandwidth if a single wireless terminal is targeted to        receive the wake-up signal, and a relatively narrower bandwidth        if a several wireless terminals are targeted to receive the        wake-up signal to be transmitted using frequency division        multiplexing (FDM).    -   19. An access point as in any one of 11-18, configured to        generate the WUS using on-off keying (OOK), and for the        relatively narrower bandwidth populating 13 sub-carriers by some        signal, and for the relatively wider bandwidth populating 52        sub-carriers by some signal.    -   20. An access point as in 19, configured to apply Manchester        coding.

Reference has been made herein to various embodiments. However, a personskilled in the art would recognize numerous variations to the describedembodiments that would still fall within the scope of the claims. Forexample, the method embodiments described herein discloses examplemethods through steps being performed in a certain order. However, it isrecognized that these sequences of events may take place in anotherorder without departing from the scope of the claims. Furthermore, somemethod steps may be performed in parallel even though they have beendescribed as being performed in sequence.

In the same manner, it should be noted that in the description ofembodiments, the partition of functional blocks into particular units isby no means intended as limiting. Contrarily, these partitions aremerely examples. Functional blocks described herein as one unit may besplit into two or more units. Furthermore, functional blocks describedherein as being implemented as two or more units may be merged intofewer (e.g. a single) unit.

Hence, it should be understood that the details of the describedembodiments are merely examples brought forward for illustrativepurposes, and that all variations that fall within the scope of theclaims are intended to be embraced therein.

The invention claimed is:
 1. A method for a wireless communicationdevice, the method comprising: detecting, by a wake-up receiver (WUR) ofthe wireless communication device, a wake-up signal (WUS) for waking upa main receiver of the wireless communication device; determining areception condition metric for the WUR based on detecting the WUS; andcontrolling a WUS bandwidth based on the reception condition metric forthe WUR, wherein: controlling the WUS bandwidth comprises transmitting,to an access point node, a control signal that is based on the receptioncondition metric; the WUS bandwidth comprises a bandwidth of a signalcomprising a further WUS that is transmitted by the access point node;and the bandwidth of the signal comprising the further WUS is responsiveto the control signal.
 2. The method of claim 1, wherein determining thereception condition metric for the WUR comprises: correlating a receivedsignal comprising the WUS with a WUS reference signal to provide anextreme correlation value; and determining the reception conditionmetric for the WUR based on the extreme correlation value.
 3. The methodof claim 2, wherein determining the reception condition metric for theWUR further comprises: comparing the extreme correlation value to areception condition threshold value; determining the reception conditionmetric to have a first reception condition value when the extremecorrelation value is higher than the reception condition thresholdvalue; and determining the reception condition metric to have a secondreception condition value when the extreme correlation value is nothigher than the reception condition threshold value.
 4. The method ofclaim 3, further comprising dynamically adapting the reception conditionthreshold value based on an immediately previous bandwidth associatedwith the WUS.
 5. The method of claim 3, further comprising: comparingthe extreme correlation value to a WUS detection threshold value that islower than the reception condition threshold; and waking up the mainreceiver when the extreme correlation value is larger than the WUSdetection threshold value.
 6. The method of claim 1, wherein the controlsignal is a WUS bandwidth request.
 7. A method for an access point nodeof a wireless network, the method comprising: receiving, from a wirelesscommunication device, a control signal that is based on a receptioncondition metric that is determined based on a wake-up receiver (WUR) ofthe wireless communication device detecting a wake-up signal (WUS) forwaking up a main receiver of a wireless communication device; andcontrolling a bandwidth of a signal comprising a further WUS based onthe control signal; and transmitting the signal comprising the furtherWUS to at least the wireless communication device, wherein the furtherWUS having the bandwidth according to the controlling.
 8. The method ofclaim 7, wherein the control signal is a first WUS bandwidth request. 9.The method of claim 8, wherein: the method further comprises receiving,from a second wireless communication device, a second WUS bandwidthrequest that is based on a second reception condition metric that isdetermined based on a WUR of the second wireless communication devicedetecting the WUS; and controlling the bandwidth of the signalcomprising the further WUS comprises selecting, as the bandwidth, amaximum of respective bandwidths indicated by the first and second WUSbandwidth requests.
 10. A wireless communication device, comprising: amain receiver and a wake-up receiver (WUR) configured to wake up themain receiver based on detection of a wake-up signal (WUS); atransmitter; and a controller operably coupled to the transmitter, themain receiver and the WUR, whereby the wireless communication device isconfigured to: detect a WUS by the WUR; determine a reception conditionmetric for the WUR based on detection of the WUS; and control a WUSbandwidth based on the reception condition metric for the WUR wherein:the wireless communication device is configured to control the WUSbandwidth based on transmitting, to an access point node, a controlsignal that is based on the reception condition metric; the WUSbandwidth comprises a bandwidth of a signal comprising a further WUSthat is transmitted by the access point node; and the bandwidth of thesignal comprising the further WUS is responsive to the control signal.11. The wireless communication device of claim 10, wherein the wirelesscommunication device is configured to determine the reception conditionmetric for the WUR based on: correlating a received signal comprisingthe WUS with a WUS reference signal to provide an extreme correlationvalue; and determining the reception condition metric for the WUR basedon the extreme correlation value.
 12. The wireless communication deviceof claim 11, wherein the wireless communication device is furtherconfigured to determine the reception condition metric for the WUR basedon: comparing the extreme correlation value to a reception conditionthreshold value; determining the reception condition metric to have afirst reception condition value when the extreme correlation value ishigher than the reception condition threshold value; and determining thereception condition metric to have a second reception condition valuewhen the extreme correlation value is not higher than the receptioncondition threshold value.
 13. The wireless communication device ofclaim 12, wherein the wireless communication device is furtherconfigured to dynamically adapt the reception condition threshold valuebased on an immediately previous bandwidth associated with the WUS. 14.The wireless communication device of claim 12, wherein the wirelesscommunication device is further configured to: compare the extremecorrelation value to a WUS detection threshold value which is lower thanthe reception condition threshold; and wake up the main receiver whenthe extreme correlation value is larger than the WUS detection thresholdvalue.
 15. The wireless communication device of claim 10, wherein thecontrol signal is a WUS bandwidth request.
 16. An access point node of awireless network, the access point node comprising: a transceiverconfigured to communication with at least one user equipment (UE); acontroller operably coupled to the transceiver, whereby the access pointnode is configured to perform operations corresponding to the method ofclaim 7.